This invention relates generally to spray coating and more specifically to a three dimensional spray coating method and simulation.
A significant problem associated with spray coating processes has been the difficulty in achieving a specified deposit thickness on a substrate surface. The following factors contribute to the difficulties in achieving the specified deposit thickness distribution: the three-dimensional part geometry; the changing characteristics of the spray gun due in part to changes in the process conditions and in part to gun aging with time; and the non-optimized robot motion spray path associated with such coating processes. At present there is no prediction tool available for designing the spray pattern or the gun motion path to accommodate a new three-dimensional part geometry.
As a particular example of a coating process, a plasma spray process involves extremely high temperatures with metal or ceramic powder being directed at a substrate surface. A vacuum plasma spray (VPS) process is used, for example, on turbine buckets to produce coatings that serve as oxidation barriers. The relative motion paths of the turbine bucket and the robot that controls the plasma spray gun are determined based on experience with previously made buckets of similar styles. Excessive experiments to verify the coating thickness distribution, however, cost both time and money.
Currently, the coating thickness distribution on turbine buckets is evaluated by a destructive technique, whereby a certain number of buckets are cut into sections, mounted, polished, and examined under a microscope to determine if their respective thickness distributions are within specified limits. If the thickness distributions are not acceptable, then the robot program or the process conditions are adjusted and the procedure is repeated. This trial-and-error approach is often repeated many times during the process development cycle, especially for new products. In new products, difficulties arise in determining optimum process conditions due to a lack of understanding concerning the interactions of the process variables, the part geometry, and the final coating quality.
Accordingly, there is a need in the art for improved evaluation and control in three dimensional coating processes.